Apparatus and method for selectively work hardening a workpiece



March 31, 1964 J- F. ORLOFF APPARATUS AND METHOD FOR SELECTIVELY WORK HARDENING A WORKPIECE Filed June 13, 1961 S Sheets-Sheet 1 INVENTOR.

J2% v f. 0 1/4764 March 31, 1964 J- F. ORLOFF 3,126,561

APPARATUS AND METHOD FOR SELECTIVELY WORK HARDENING A WORKPIECE Filed June 115, 1961 3 Sheets-Sheet 2 $4 444 7 A744 INVEN TOR. 44 41 J14 27, )1 07/0/74 March 31, 1964 J.,F. QRLOFF 3,126,561

APPARATUS AND METHOD FOR SELECTIVELY WORK HARDENING A WORKPIECE Filed June 15, 1961 I s Sheets-Sheet a I Q Q $3 v A INVENTOR.

United States Patent Ofiice 3,126,561 Patented Mar. 31, 1964 3,126,561 APPARATUS AND METHOD FOR SELECTIVELY WGRK ENING A WORKPIECE John F. Orlotf, Mount Clemens, Mich., assignor to Huck Manufacturing Company, Detroit, Micln, a corporation of Michigan Filed June 13, 1961, Ser. No. 116,835 9 Claims. (Cl. 1011) This invention relates to means and methods for selectively work hardening a workpiece to provide a hardness gradient at a preselected location.

The present invention is described in conjunction with the application of work or strain hardening to hollow rivets used to fasten a pair ofplates. The hollow rivets referred to have a sleeve portion which is inserted through aligned apertures in a pair of plates and a head portion which abuts one of the plates. An axial compressive force is applied between the end of the sleeve and the head, causing the sleeve to yield at a predetermined force, thereby forming a bulbed or blind head which secures the two plates together. In order to be certain that the plates are properly gripped, the bulbed head must be formed at the proper point on the sleeve. Usually the end of the sleeve has been cold worked to some extent during the cold heading process in the formation of the rivet, thus providing that portion with a higher tensile strength and a higher yield point than the rest of the sleeve. The formation of the bulb or head begins at the weakest point on the sleeve or at a point just beyond the cold worked portion. It would be advantageous, for a purpose to be described, if the work hardened area of the sleeve portion could be increased. With present methods and apparatus, the amount of work hardening applied to the sleeve portions is limited; therefore, it is an object of this invention to provide a method for 1n creasing that area of the sleeve portion of a rivet which is work hardened.

It is another object of this invention to provide means for increasing that portion of the sleeve portion of a rivet which is work hardened.

It is an object of this invention to provide a novel method for providing work hardening in a part.

It is still another object of this invention to provide novel means for providing work hardening in a part.

Other objects, features, and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a side elevational view of apparatus during one step of an operation for providing work hardening in accordance with the present invention with some parts shown broken away and some parts shown in section;

FIG. 2 is a view of the apparatus of FIG. 1 during a second step;

FIG. 3 is a view of the apparatus of FIG. 1 at a later stage of the second step shown in FIG. 2;

FIG. 4 is a view of the apparatus of FIG. 1 during a third step;

FIG. 5 is a side elevational view of a modified structure prior to a first step of an operation for providing work hardening in accordance with the present invention with some parts shown broken away and some parts shown in section;

FIG. 6 is a view of the apparatus of FIG. 5 during a first step;

FIG. 7 is a view of the apparatus of FIG. 5 during a second step;

FIG. 8 is a view of the apparatus of FIG. 5 at a later stage of the second step; v

FIG. 9 is an elevational view illustrating the eifect of increased work hardening with relation to the minimum grip length of a rivet;

FIG. 10 is a blown up view of a rivet shown in FIG. 9 and particularly of the area on that rivet indicated by the numeral 10; and

FIG. 11 is a blown up view of a different rivet shown in FIG. 9 and particularly of the area on that rivet indicated by the numeral 11.

In general, in this invention an increased portion of a rivet is work hardened by providing an annular groove in a die into which material from a sleeve of the rivet can be caused to cold flow. Subsequently, upon ejection of the rivet from the die, the material in the groove is caused to cold flow back into the sleeve portion. The area in which this cold flow or cold work occurs has a higher tensile (and compressive) strength and yield point than the remainder of the sleeve; with this method and apparatus this area of cold Work is considerably greater than that obtained by the conventional cold heading process. The basic method and apparatus of this invention can be utilized to provide an increased cold worked area in a rivet either during the cold heading operation of a solid blank in the formation of a rivet or to a hollow rivet after the cold heading operation.

FIGS. 1-4 depict the various steps and stages in the cold heading of a blank in which increased cold working is obtained. FIG. 1 depicts a first stage in the formation of a rivet generally designated by the numeral 12 from a solid blank or workpiece. The apparatus shown therein comprises a fixed base member 13 having a bore 22 with a stop member 14 disposed axially inwardly therein wtih a reduced diameter portion 15 on the member 14 facing axially outwardly. A movable die 24 is slidably disposed within the bore 2?. and is biased axially outwardly by means of a coil spring member 32 which is partially dis posed about the reduced diameter portion 15 and is compressively preloaded with one end bearing against the movable die 24 and the other end bearing against the stop member 14. The movable die member 24 is retained in the bore 22 by means of a round pin 34 having its diameter extending radially inwardly into the bore 22 and being engageable with a shoulder 36 in a transverse slot 38 located in the outer surface of the movable die member 24-. The slot 38 allows axial movement of the movable die 24 relative to the pin 34 while the shoulder 36 limits axial movement by engagement with the pin 34. A bore 16 in the fixed base 13 is in alignment with a bore 18 in the stop member 14 and a bore 26 in the movable die member 24. The bore 26 has an annular groove 28 of a predetermined width and depth for a purpose to be described. The groove 28 which terminates in chamfered or inclined faces 30 is located a predetermined distance from the outer surface 23 of the movable die 24, depending upon the grip length of the rivet 12 or upon the length of the shank 54.

The bores 16, 18, and 26 are of the same diameter and receive a shank 42 of a movable knockout pin 40. The shank 42 terminates in a shoulder 44 having an outwardly extending cone portion 46 disposed thereon.

In operation, a solid blank is inserted into the bore 26. In a first step, the knockout pin 40 is held stationary with the shoulder 44 and cone or head 46 in a predetermined positional relationship relative to the groove 28. The first blow is struck by a ram member 48 the force of which is reacted by means of the knockout pin 40 causing the initial formation of a head 50 on the rivet 12. Looking now at FIG. 2, in a second step, as a second blow is applied to the rivet 12 by means of a heading die 52, a portion of the load is now carried by the head 56 which is partially formed. Thus, as the head 50 begins to take shape, a part of the axial load from the heading die 52 is taken by the spring member 32 and by the movable die member 24 as well as by the knockout pin 40. Notice in FIG. 2 that during the second blow the head 50 is formed and some material from what is now a shank 54 of the rivet 12 is forced into the annular groove 28. FIG. 3 shows the rivet 12 at an instant later at the completion of the second blow when the head is completely formed and the annular groove 28 is completely filled with material from the shank 54. Thus the shank 54 as shown in FIG. 3 has formed at its lower end an annular ring portion 56 and a conical depression 58.

Upon completion of the heading operation, ejection of the rivet 12 is initiated and the knockout pin 40 is moved axially in the aligned bores 16, 18, and 26 forcing the rivet 12 out of the bore 26 in the movable die member 24. As this is done, the material in the annular ring 56 in the groove 28 is extruded on to the shank portion 54 of the rivet 12, thereby causing further work hardening in that area. The area of the shank portion 54 which is work hardened is dependent upon the width of the groove 28 while the depth of work hardening is dependent upon the depth of the groove 28.

Without the annular groove 28 some portion of the shank 54 would be work hardened by virtue of the blow caused by the cone portion 46. However, it can be seen that by the apparatus and method just described, that portion of the shank 54 which is work hardened is increased.

The method and apparatus as previously described is for use in the cold heading of a rivet from a solid blank. The solid rivet formed thereby can then be pierced or drilled to form a hollow rivet and set in the manner described. It is also desirable that cold working be increased on the shank of a rivet after it has been cold headed and pierced or drilled. The method and apparatus for increasing the cold worked area in a preformed rivet is shown in FIGS. 58

Looking now to FIG. 5, a hollow rivet 12a has a shank portion 42a, a head 50a, and an axial bore 60a therethrough. The apparatus esesntially comprises a stop member 14a secured within a bore 62 in a fixed base 13a by means of a pair of set screws 64. The stop member 14a has a centrally disposed bore 18a terminating at its outer end in a reduced diameter bore 19. The fixed base 13a has an enlarged bore 22a which is substantially concentric with the bore 62 and which terminates in an annular shoulder 66 at the juncture with the bore 22a. A movable die member 24a has an enlarged diameter portion 25 slidably disposed within the enlarged bore 22a and a reduced diameter portion 27 slidably disposed within the bore 62. A shoulder 68 formed at the juncture of the sections 25 and 27 is matable with the shoulder 66 in the fixed base member 12a.

The movable diameter 24a is maintained axially outwardly by means of a compressively biased coil spring 32a which bears against the portion 27 and the stop member 14a. The movable die member 24a is maintained within the bore 22a by means of a round pin 34a having its diameter extending radially inwardly into the bore 22a and being engageable with a shoulder 36a of a transverse slot 38a disposed in the periphery of the enlarged portion 25. Thus the spring member 32a maintains the movable die member 24a axially outwardly with the shoulder 36a in contact with the pin 34a.

The movable die 24a has a centrally disposed bore 26a in the outer end of the enlarged diameter portion 25 in communication with an enlarged bore 70 extending through the remainder of the die member 24a. A shoulder 71 is defined by the juncture of the coaxial bores 26a and 70. The bore 26a has a diameter equal to the diameter of the shank 42a of the rivet 12a and has an annular groove 28a which terminates in a chamfered face 30a. The groove 28a is located a predetermined distance from the outer surface 23a of the movable die 24a, depending upon the grip length of the rivet 12a or upon the length of the shank 54a.

An ejection member 72 having an axial bore 76 has an enlarged portion 74 slidably disposed within the bore 70 and has a reduced diameter portion 77 which is matable with the bore 28a. A shoulder 79 is formed at the juncture of the portions 74 and 77. A floating sizing pin 40a has a sizing head 78 at one end of a shank portion 42a which is slidably disposed within the bore 76 in ejection member 72. The shank 42a is also slidably disposed within the reduced diameter bore 19 in the stop member 14a. At the opposite extremity from the sizing head 78 is an enlarged head portion 82 which is slidably disposed within the enlarged diameter portion 18a of the stop member 14a. The ejection member 72 is engaged at the extremity of the enlarged portion 74 by a plurality of rods 86 passing through aligned holes in the end of the fixed base 13a and the stop member 14a. The rods 86 are movable axially by means of a ram (partially shown).

In FIG. 5 the rivet 12a is shown seated in the bore 26a in the movable die 24a and the ram 52a is shown just in engagement with the rivet head 50a. At the same time the ejection member 72 is in a retracted position as shown and the floating sizing pin 40a is at the extremity of the bore 18a and in engagement with the rear portion of the fixed base 13a. Upon axial inward movement of the ram 52a, an axial force is applied to the movable die member 24a such as to compress the spring 32a and cause axial inward movement of the movable die member 24a until the sizing head 78 is injected into the bore 60 at the end of the shank 42a of the rivet 12a. The sizing head 78 is chamfered at its extremity to a reduced diameter portion 84 so as to facilitate insertion of the sizing head 78 within the diameter 60. As the sizing head 78 is inserted into the bore 60 the material in that portion of the shank 54a is caused to flow through the aperture defined by the sizing head 78 and the groove 28a into the annular groove or cavity 28a. The dimension of the aperture so defined is substantially equal to the final wall thickness desired in the cold worked portion of the shank 42a of the rivet 12a. Upon completion of the stroke the shoulder 68 on the movable die member 24a is in abutment with the shoulder 66 on the fixed base member 13a and the sizing head 78 has been inserted into the bore 60 of rivet 12a and has forced the material at the lower end of the shank 42a into the groove 28a. The apparatus at that time has the position as shown in FIG. 6. Next the ejection of the rivet 12a is commenced.

Looking now to FIG. 7, the die member 52a is being being retracted from the head 50a of the rivet 12a, thus allowing the movable die 24a to be moved axially outwardly by the force of the spring 32a until the shoulder 36a is in engagement with the pin 34a. The ram 85 is actuated to move the rods 86 causing the ejection member 72 to be moved axially outwardly such that the reduced diameter portion 77 is moved into the end of the bore 26a in the die member 24a and into engagement with the end of the shank or sleeve 42a of rivet 12a. Note that when the movable die member 24a is carried to its extreme outward position the sizing pin 40a is also carried to its extreme position such that the enlarged head portion 82 is in engagement with the reduced diameter portion 19. The pin 40a is carried there by the adhering force between the expanded portion of the sleeve 42a and the sizing head 78. Additional axial force applied to the ram 85 and hence the rods 86 causes the ejection member 72 to be moved further axially until the rivet 12a is ejected from the bore 26a in the movable die 24a. At this time the shoulder 79 on ejection member 72 is in abutment with the shoulder 71 on the die member 24a. As the rivet 12a is ejected, the shank 42a is forced to assume the configuration or diameter of the bore 26a. As this occurs, the metal is caused to cold flow through the aperture defined by the chamfered portion 84 of the sizing head 78 and the chamfered portion 30a of the annular groove 28a; thus the metal in that portion of the sleeve 42a of the rivet 12a is work hardened thereby increasing its tensile strength.

Upon ejection of the rivet 12a from the bore 26a, the ejection member 72 can be retracted to its normal position and another rivet can be cold worked in a similar manner.

The effect of cold working by the apparatus and methods previously described can be best seen in FIGS. 9-11. In FIG. 9 a rivet 1212, work hardened by conventional methods, is shown having a cold worked portion on the sleeve or shank 42b generally shown by the shaded area designated by the numeral 9012. FIG. 10 more graphically shows the cold worked portion 90b on the shank 42b of the rivet 1212. A rivet 12c, having identical physical dimensions with the rivet 12b but having been work hardened in accordance with the invention as described, by comparison has a work hardened portion generally indicated by the numeral 990 (shown more graphically in FIG. 11). In FIG. 9, the rivet 12b is shown securing a plurality of plates W of a combined thickness D with the sleeve 42b having a blind head formed thereon by means previously discussed. The thickness D, in this case, also indicates the minimum grip of that particular fastener with the formation of the blind head being initiated at an area beyond that which was work hardened. A similar rivet, 12b, however, having the same amount of Work hardening and of course the same minimum grip, if applied to a second plurality of plates W having a smaller combined thickness D, will form the head at a point removed from the plates W and hence will not provide a tight clinching force. This is important since it is usually desired that the plates W and W be tightly fastened together. In a case such as this, a rivet having a shorter grip length is required. However, with a rivet such as 120 having an increased portion of work hardening 9th, not only will the plates W of a combined thickness D be accommodated, but also the plates W, since the head will be properly formed with the smaller thickness and hence, shorter grip length D (FIG. 9). Thus, in this case, a rivet having an increased work hardened portion in accordance with the method and apparatus of this invention can be used with plates of a smaller combined thickness than a conventionally cold worked rivet. This means that an economy can be realized in that rivets having increased work hardening can be stored in larger quantities in a minimum number of grip lengths or, in other Words, fewer difi'erent grip lengths need be stored.

The above discussion has been specifically related to a hollow rivet having a head and a shank in which the cold Worked portion is increased in order that a blind or bulbed head can be formed at a desired point. However, the benefits of such work hardening can be applied to other types of rivetsfor example, the type in which the blind head is formed by axially splitting the end of the shank. The benefits of such work hardening could also be applied to a simple tubular member i.e. a pipe, etc. Thus while it will be apparent that the preferred embodiments of the invention disclosed are well calculated to fulfill the objects above stated, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. Apparatus for work hardening a hollow workpiece comprising a movable die member having a bore for receiving the workpiece, said bore having an annular groove therein, a pin member terminating at one end in a head portion and being movable relative to said movable die member in said bore, means for applying an axial force to the workpiece and to said movable die member for moving said movable die member axially inwardly relative to said pin member causing insertion of said head portion into the workpiece for flowing the material of the Workpiece into said annular groove, and ejection means indeendent of said pin member for moving the workpiece axially outwardly from said bore in said movable die member causing the material in said annular groove to flow back to substantially the configuration as defined by said bore.

2. Apparatus for work hardening a hollow workpiece comprising a movable die member having a bore for receiving the workpiece, said bore having an annular groove therein, a pin member movable in said bore in said movable die member and terminating at one end in a head portion having a diameter larger than the internal diameter of the hollow workpiece, means for applying an axial force to the workpiece and to said movable die member for moving said movable die member axially inwardly relative to said pin member causing insertion of that head portion into the workpiece for flowing the material of the workpiece through an aperture defined by said head portion of said pin member and said annular groove into said annular groove, and ejection means independent of said pin member for moving the workpiece axially outwardly from said bore in said movable die member causing the material in said annular groove to flow back through said aperture to substantially the configuration as defined by said bore.

3. The apparatus of claim 2 with said aperture being substantially equal to the wall thickness of the workpiece.

4. The apparatus of claim 2 with said ejection means comprising a tubular member having a portion with an outside diameter substantially equal to the diameter of said bore, said tubular portion disposed about said pin member and being movable axially within said bore relative to said pin member and engageable with the workpiece for moving the workpiece axially outwardly from said bore.

5. Apparatus for work hardening a hollow workpiece comprising a fixed base member having an axial bore therein, a movable die member slidably disposed within said axial bore and having a bore for receiving the workpiece, said bore having an annular groove therein, spring means urging said movable die member axially outwardly of said axial bore in said fixed base member, limit means operatively associated with said fixed base member and said movable die member for limiting the axially outward movement of said movable die member in said axial bore in said fixed base member, a floating pin member terminating at one end in a head portion and being movable in said bore in said movable die member, ram means for applying an axial force to the workpiece and to said movable die member for moving said movable die member axially inwardly in said axial bore in said fixed base member relative to said floating pin member causing insertion of said head portion into the workpiece for flowmg the material of the workpiece into said annular groove, sald spring means forcing said movable die member and the workpiece outwardly against said limit means upon removal of the axial force by said ram means, said floatmg pin member being movable axially outwardly within the workpiece with said movable die member, means for hunting the axial outward movement of said floating pin member, and ejection means independent of said pin member for moving the workpiece axially outwardly from said bore in said movable die member causing the material in said annular groove to flow back to substantially the configuration as defined by said bore in said movable die member.

6. The method of work hardening a solid workpiece comprising the steps of locating the workpiece in a bore having an annular groove and against one end of an abutment located within the bore, moving the workpiece relatively to the abutment to cold flow the material of the workpiece to completely fill the cavity defined by the bore, the annular groove, and the abutment and confining the end of the workpiece within the bore to prevent axial flow thereof, and with the end of the workpiece so confined to prevent axial flow of the workpiece farther into the bore, cold flowing the material of the workpiece from the groove back into the workpiece while ejecting the workpiece from the bore.

7. The method of work hardening a selected portion of the shank of a hollow rivet comprising the steps of locating the shank of the rivet in a bore of substantially the same diameter as the shank with the bore having an annular groove, providing an abutment in the bore and moving the shank telescopically over the abutment in a region adjacent the annular groove in the bore to radially expand the selected portion of the shank of the rivet into the annular groove, and with the abutment located in a position in the bore adjacent the groove to define a restricted annular space, cold flowing the material of the shank of the rivet from the groove through the restricted annular space into substantially the configuration as defined by the bore while ejecting the rivet from the bore.

8. The method of work hardening a predetermined portion of the end of the shank of a hollow rivet comprising the steps of locating the shank of the rivet in a bore having an annular groove, providing an abutment in the bore concentrically with the groove to define therewith a restricted annular aperture and moving the shank telescopically over the abutment and through the aperture to radially expand the predetermined portion of the end of the shank into the groove, and cold flowing the material of the shank of the rivet from the groove back through the aperture into substantially the configuration as defined by the bore while ejecting the workpiece from the bore.

9. The method of cold forming a rivet having a head and a shank from a solid workpiece and of work hardening the end of the shank comprising the steps of locating the workpiece partially Within a bore having an annular groove and against one end of an abutment located within the bore, striking the workpiece with a first blow relative to the abutment thereby partially forming a head from that portion of the workpiece outside of the bore having a shank formed from that portion of the workpiece located within the bore and cold flowing some material from a predetermined portion at the end of the shank into the annular groove, striking the workpiece with a second blow thereby finally forming the head and moving the workpiece relative to the abutment to cold flow additional material from the predetermined portion at the end of the shank to completely fill the remainder of the cavity defined by the bore, the abutment and the annular groove and confining the end of the predetermined portion at the end of the shank within the bore to prevent axial fiow thereof, and with the predetermined portion at the end of the shank so confined to prevent axial flow thereof farther into the bore, cold flowing the material of the shank from the groove back into the shank while ejecting the workpiece from the bore.

References Cited in the file of this patent UNITED STATES PATENTS 1,236,470 Neuberth Aug. 14, 1917 1,797,702 Pierre Mar. 24, 1931 2,030,169 Huck Feb. 11, 1936 2,090,338 Tomalis Aug. 17, 1937 2,261,318 Wilcox NOV. 4, 1941 

1. APPARATUS FOR WORK HARDENING A HOLLOW WORKPIECE COMPRISING A MOVABLE DIE MEMBER HAVING A BORE FOR RECEIVING THE WORKPIECE, SAID BORE HAVING AN ANNULAR GROOVE THEREIN, A PIN MEMBER TERMINATING AT ONE END IN A HEAD PORTION AND BEING MOVABLE RELATIVE TO SAID MOVABLE DIE MEMBER IN SAID BORE, MEANS FOR APPLYING AN AXIAL FORCE TO THE WORKPIECE AND TO SAID MOVABLE DIE MEMBER FOR MOVING SAID MOVABLE DIE MEMBER AXIALLY INWARDLY RELATIVE TO SAID PIN MEMBER CAUSING INSERTION OF SAID HEAD PORTION INTO THE WORKPIECE FOR FLOWING THE MATERIAL OF THE WORKPIECE INTO SAID ANNULAR GROOVE, AND EJECTION MEANS INDEPENDENT OF SAID PIN MEMBER FOR MOVING THE WORKPIECE AXIALLY OUTWARDLY FROM SAID BORE IN SAID MOVABLE DIE MEMBER CAUSING THE MATERIAL IN SAID ANNULAR GROOVE TO FLOW BACK TO SUBSTANTIALLY THE CONFIGURATION AS DEFINED BY SAID BORE. 